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<pre wrap="">But now I get this error message :
unsaved editor&gt;:27:23: function call: expected a function after the open parenthesis, but found a part in: (tarief1 amount)

When I do (tarief 1 amount) instead of ((tarief amount))
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<pre wrap="">Yes, that's where the syntax error is. So you've fixed that.</pre>
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I fixed that?&nbsp; I always thought that if I use another function that
I must be into ().<br>
So In my opinion one () for the then part and one () for the
function call. <br></div></blockquote><div><br></div>No, there is no pair of parentheses for the "then" part, only one for the function call.</div><div><br></div><div>(cond [question answer]</div><div>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;[question answer]</div><div>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;...</div><div>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;[question answer])</div><div>where each question and each answer is an expression (usually a function call).</div><div><br><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000"><blockquote cite="mid:C462650F-784E-463B-B671-61FF7B1BCDC9@adelphi.edu" type="cite"><pre wrap="">1) Have you written a complete set of test cases, with right answers, using "check-expect"? Since there are four categories of input for this problem, you need at least four test cases, and you should probably have three more for the boundaries, a total of seven test cases.
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Nope, check-expect is not explained on chapter section 3 of the book
how to design programms. So I did not use that function.&nbsp; I can make
test-cases but then in this form <br>
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(<span class="builtin">=</span> (<i>tarief 495</i><span class="selfeval"></span>) 1,2375) <br></div></blockquote><div><br></div>That should work too, although it's not as convenient. &nbsp;Make sure you put a bunch of those test cases in the Definitions pane, after the definition:</div><div><br></div><div>(define (tarief blah blah)</div><div>&nbsp; &nbsp;blah blah blah</div><div>&nbsp; &nbsp;)</div><div><br></div><div>(= (tarief 495) 1,2375)</div><div>(= (tarief 0) 0)</div><div>(= (tarief 100) whatever)</div><div>...</div><div><br></div><div>That will also solve the next problem:</div><div><br></div><div><blockquote type="cite"><div bgcolor="#FFFFFF" text="#000000">3) Have you used the Stepper to watch what your program is doing?
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Yes, when I do (payback 2600) on the prompt and press Step I only
see a message&nbsp; All definitions have been sucessfully evaluated and
not other outcome so that did not help me any further. <br></div></blockquote></div><br><div>The Stepper only works on expressions in the Definitions pane, not the Interactions pane. &nbsp;If you put your test cases in the Definitions pane as described above, the Stepper will help you find where things are going wrong.</div><div><br></div><div>BTW, check-expect is not discussed in _How to Design Programs_ because it hadn't been invented yet when the book was written. &nbsp;It's quite easy to use, though: replace the = sign in the above tests with check-expect, and when you hit "Run" you'll get a report of which of your test cases worked, the expected answer and the actual answer.</div><div><br></div><div>You might consider working through the Second Edition of _How to Design Programs_ instead; see&nbsp;<a href="http://www.ccs.neu.edu/home/matthias/HtDP2e/">http://www.ccs.neu.edu/home/matthias/HtDP2e/</a> .</div><div><br></div><br><br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Helvetica; font-size: medium; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><div>Stephen Bloch</div><div><a href="mailto:sbloch@adelphi.edu">sbloch@adelphi.edu</a></div></div></span></span>
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